1: The process flow of selective welding includes: flux spraying, circuit board preheating, immersion welding, and drag welding. The flux coating process plays an important role in selective welding. When welding is heated and completed, the flux should have sufficient activity to prevent bridging and oxidation of the circuit board. The flux spraying is carried by an X/Y robotic arm above the flux nozzle on the circuit board, Spray flux onto the soldering position of the double-sided circuit board.

　　2: The most important aspect of microwave peak selection welding after reflow soldering is accurate flux spraying. Micro hole spraying will never contaminate the area outside the solder joint. Micro point spraying has a minimum flux point pattern diameter greater than 2mm, so the precision of the flux position deposited on the circuit board is ± 0.5mm to ensure that the flux always covers the soldered area.

　　3: The process characteristics of selective soldering can be understood by comparing it with wave soldering. The most obvious difference between the two is that the lower part of the circuit board in wave soldering is completely immersed in the liquid solder, while in selective soldering, only certain specific areas come into contact with the solder wave. As the circuit board itself is a poor heat conducting medium, it does not heat and melt the solder joints in adjacent components and circuit board areas during soldering.